Printing on anodized aluminum



Dec. 16,1969 C(B. BLAKE m1. 3,484,

PRINTING 0N ANODIZED ALUMINUM Filed Aug. 5. 1966 u l2 I37 l4; l5

TRANSFER AN 0: E RIN E R o z N s -0 Y (QNCE) SEAL FIG. 3

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ANODIZE RINSE DRY MASK DIP FIX MASK UNMASK FIX mp MASK A UNMASK V 24 I25 2e 23;

mp FIX UNMASK w MASK N FIG. 4

SEAL UNMASK FIX mp INVENTORS CARL B. BLAKE United States Patent3,484,342 PRINTING 0N ANODIZED ALUMINUM Carl B. Blake, Bronx County, andAdolph Fuerst, Kings County, N.Y., assignors to Martin-MariettaCorporation, New York, N.Y., a corporation of MarylandContinuation-impart of application Ser. No. 252,311, Jan. 18, 1963. Thisapplication Aug. 5, 1966, Ser. No. 570,593

Int. Cl. C23b 9/02; C231. 17/00; B44c 1/04 US. Cl. 204-18 7 ClaimsABSTRACT OF THE DISCLOSURE A process for decorating aluminum comprisinganodizing said aluminum to provide a porous anodic surface. The porousanodic surface is then contacted with a sheet having printed matterthereon, said printed matter comprising a heat volatile coloring agent.The assembled anodic surface and sheet is then heated to cause transferof the printed matter. Thereafter the anodized surface is sealed.

This application is a continuationin-part of application Ser. No.252,311, filed Jan. 18, 1963, now abandoned.

The present invention relates to a process for decorating anodizedaluminum surfaces and, more particularly, to a process wherein heattransfer of ink impress-ions onto anodized aluminum surfaces is employedas one step thereof. The invention is especially directed to theapplication of complex patterns, particularly those in which numerouscolors are included to the anodized aluminum surface. Subsequent todecoration the colored anodized aluminum surface is sealed as byprolonged immersion in boiling water, the colored pattern upon thealuminum surface being resistant to such boiling and preferably also toprolonged exposure to light to provide reasonable resistance to fading.

The present invention employs the dye heat transfer process disclosed inthe application of Carl B. Blake, Ser. No. 115,152, filed June 6, 1961,now abandoned, the disclosure of said application being incorporatedherein by reference.

In accordance with the present invention, a surface of material,preferably paper, which has been printed in mirror image of the designto be produced with an ink comprising a partially sublimable coloringagent is placed in close proximity with, and preferably in directcontact with, an anodized aluminum surface and heat is applied to causeprogressive gasification or sublimation of the coloring agent to producea distinct image by condensation of the gases generated on the anodizedaluminum surface within a short period of time, desirably within 15seconds. Heat is applied at a temperature of from 140500 F., especiallyfrom 250-450 F.

The invention is illustrated by the drawing in which:

FIG. 1 is a view in cross section of the color stage of the presentinvention;

FIG. 2 is a cross-sectional view of the product of the presentinvention;

FIG. 3 is a schematic outline of the steps employed in connection withthe present invention; and

FIG. 4 is a schematic outline of steps employed in prior art processes.

A feature of the invention is the finding that sulfuric acid anodizedaluminum surfaces (including the anodized surfaces of alloys containingat least about 80% aluminum) are unusually receptive of the sublimationdyes in accordance with the invention. It has further been found thatcertain dyes are unusuall substantive toward the anodized aluminumsurface so as to provide a degree of light fastness which is unusual fordyes which sublime at moderate temperature. Indeed, it is clear that achemical association is formed between preferred sublimed dyes inaccordance with the invention and the anodized aluminum surface because,and even prior to scaling, organic soluble dyes are not significantlydissolved away from the aluminum surface by the very organic solvents inwhich they are highly soluble.

As an unusual facet of the present invention, transfer of dye to theanodized aluminum receiving surface is achieved through the use of heat.Nevertheless, and despite transfer to the anodized aluminum surface bysublirnation and condensation, it has been found that the dye issufficiently retained, especially by sulfuric acid anodized aluminumsurfaces, to resist prolonged exposure to boiling water, except Wherethe dye per se is hydrolyzable by contact with water.

Referring more particularly to the coloring of anodized aluminumsurfaces by prior art methods, the conventional surface coatings whichsit on top of the anodized aluminum surface, are subject to filmdeterioration, they can be removed by abrasion, and are often opaque,or, even when transparent, the conventional coatings detract somewhatfrom the beauty of the aluminum surface itself. Because of the extremelyminute nature of the pores in anodized aluminum surfaces, most lacquers,varnishes or the like applied to an anodized surface do not penetrateinto the pores. Such lacquers, varnishes, etc, merely form, for the mostpart, a surface layer which, as mentioned before, can be abraded orWashed away.

Anodized aluminum surfaces have also been colored by dyeing, usually bydipping the aluminum surface in the dye to provide a single overallcolor. llt is also possible to apply a resist to prodetermined areas ofthe aluminum surface followed by dipping in the dye and one, or possiblytwo colors can be applied in this manner. However, it is necessary toremove the resist and, as a result of the difficulty of this step, theapplication of several colors becomes extremely cumbersome anduneconomical. If sufiicient colors are to be applied in a pattern whichis very intricately related, as in the multi-color printing ofphotographs using half-tone technique, the required registration makesthe sequential application of resist and dye dip in a repetitive mannersubstantially impossible.

One method for the multi-color printing of aluminum surfaces which hasachieved some overall success is disclosed in United Stated Patent2,614,912 in which dyes are applied by direct printing upon the aluminumsurface. However, those familiar with anodizing and sealing of aluminumsurfaces tend to shy away from printing operations. Also, it isnecessary in the process of said patent to remove the ink by a Washingoperation which would tend to slow a fast production line. Accordingly,there is a very real need for improved processes enabling the efficient,economical and attractive multi-color finishing of aluminum.

Part of the problem solved by the present invention is the production ofhigh quality multi-color prints on sur faces which are not readilyadapted to pass through printing machinery. If one skilled in the artsof printing and anodizing were faced with the problem of producing highquality printing on an anodized surface of a massive object, forexample, an aluminum sphere, even the highest skill in the known artswould be of little one. The skilled artisan would be forced to use crudemethods, e.g. silk screens, to stencil his design. While they are veryuseful, silk screens produce a low quality print when compared to thequality of prints produced by lithography, gravure, letterpress and likemethods. By means of the present invention a relatively unskilled personcan transfer a highly sophisticated quality print to any anodizedaluminum surface upon which he can temporarily fasten a sheet, strip orpatch of transfer substrate, e.g. paper, plastic or the like. Theskilled artisan would have to provide a stencil for each color appliedand provide some means for registering each of the stencils to provide aclear total image. By means of the present invention all colors areapplied to the anodized surface at one time. Registration is providedfor on a cheap paper substrate in the manner normal to the printing art.Printed transfer sheets can be stored for substantial periods of timeenabling both the most efficient use of valuable press time andadaptability in metal decoration. The transfer of the alreadyregistered, high quality design from the transfer sheet to the anodizedaluminum surface is practically foolproof. Thus the present inventionprovides not only a process for accomplishing what could not be donebefore, but also provides, at the same time, a process which practicallyeliminates decoration rejects on valuable, anodized surfaces.

In accordance with the present invention, a printable surface, e.g. asheet of material, is printed, preferably by offset printing, in mirrorimage of the desired design (including letters, pictorial matter,abstracts, etc.) with an ink which comprises a coloring agentconstituted by a non-hydrolyzable, water insoluble dye having thefollowing sublimation characteristics:

(A) No noticeable sublimation below 120 F.;

(B) A sublimation half-life at 500 F. of less than 75 seconds; and

(C) A sublimation half-life at a temperature in the range of from 140 F.to 500 F. of from 0.575 seconds. Preferably, the desired sublimationhalf-life of the coloring agent exists at a temperature in the range offrom 180 F. to 450 F., and most preferably in the range of from 250 F.to 425 F. to provide a print in mirror image of the design to beproduced.

The term sublimation half-life designates the time required for a 50%weight loss through elimination of part of the coloring agent as aresult of its conversion to the gaseous state.

Since the ink impression to be formed is a thin film (usually 3-5microns in thickness), the surface area per unit weight is very largeand the characteristics of the coloring agent referred to are measuredwith the coloring agent in any convenient form with a similar very largesurface area to weight ratio.

In accordance with the invention, it has been found that certain dyesare unusually substantive, especially to sulfuric acid-anodized aluminumsubstrates, these dyes falling within the following categories:

(1) Anthraquinone dyes having in the 1, 4, 5 or 8 position a hydrogensubstituent, or an hydroxyl substituent, or a nitrogen atom carrying anactive hydrogen atom, said nitrogen atom being present in the form of anamine or an amide. The other substituent on the nitrogen atom may be anyhydrocarbon.

(2) A dyes having a hydrogen atom in the position ortho to the azogroup; and

(3) Dyes containing the 1,3 indandione group.

It should be understood that the specific types of dyes referred toabove are still required, in accordance with the invention, to possessthe required sublimation characteristics and to be non-hydrolyzable inorder that they may be applied to the anodized aluminum surface bysublimation and resistance to the boiling water treatment required inconnection with the sealing of the anodized aluminum surface.

It is desired to emphasize that the inks which are employed should notinclude wax or other meltable component since this would cause the heattransfer process to include mechanical transfer of the meltablecomponent which would interfere with the process of the invention.

Preferred dyes which have been found to be substantive to the anodizedaluminum surface in accordance with the present invention, andreasonably resistant to destruction by boiling water, are illustrated bythe following dyes.

A suitable anthraquinone dye is Quinizarine Green Base described in theColour Index as C. I. Solvent Green 3 and identified by C. I. No. 61565.This dye contains an hydroxyl group in the 1 position and an amino groupon the 4 position. Similar anthraquinone dyes in which either the aminoor the hydroxyl substituent is present are also useful. The amino groupmay be a primary amino group in which the two reactive positions on thenitrogen atom are occupied by a hydrogen or one of the hydrogen groupsmay be reacted with an organic carboxylic acid to form an amide such asby reaction with acetic acid or benzoic acid or one of the hydrogens canbe substituted by any monofunctional hydrocarbon radical such as loweralkyl and aryl groups so long as the substituent forming the secondaryamine is not so long as to interfere with the desired sublimationcharacteristics of the dye which have been defined.

Suitable disazo dyes are illustrated by Sudan Yellow GRA conc. describedin the Colour Index as C. I. Solvent Yellow 30 and identified by ColourIndex No. 21240. This dye contains an hydroxyl group ortho to each ofthe two azo groups in the dye.

Dyes containing the 1,3 indandione group and which are sublimable inaccordance with the invention are illustrated by Quinoline Yellow Basedescribed in the Colour Index as C. I. Solvent Yellow 33 and identifiedby Colour Index No. 47000.

As pointed out in the application of Blake referred to hereinbefore, theink containing the sublimable dye in accordance with the inventioncomprises an organic resinous binder which, when deposited either withor without the use of moderate heat, supplies a dry solid film whichremains solid and dry upon exposure to the elevated temperature transferconditions which are employed.

The invention will be illustrated by the following example.

EXAMPLE Each of the dyes specifically referred to hereinbefore wasformulated into a printing ink as follows:

Parts by weight Long oil linseed-isophthalic alkyd 1 12.50 Mediumviscosity linseed oil 25.00 Heavy viscosity linseed oil 12.50 Calciumcarbonate extender pigment 30.00 Dye 20.00

An alkyd of equimolar proportions of glycerin and isopllthalic acidcontaining 65% by weight of linseed oil.

These components are stirred together and then milled on a 3 roll milluntil the mixture has a grind gauge of 3. The ink so-produced wasprinted on thin paper on an offset press and is dry to the touch in avery few minutes and thoroughly dry in about 4-8 hours. The dry print isplaced over a sulfuric acid anodized aluminum surface and pressedslightly with a heated hand iron set at 400 F. for a period of 6seconds. In each instance, and using each of the dyes referred tohereinbefore, a true, clear and clean image was produced on the anodizedaluminum surface. Despite the fact that these inks are soluble inorganic solvents such as methyl ethyl ketone, immersion of the printedanodized aluminum surface in methyl ethyl ketone for a period of twohours does not significantly affect the quality of the image. When thefreshly printed anodized aluminum surface is placed in boiling water for/2 hour, the quality and clarity of the dye remained acceptable and theanodized aluminum surface was effectively sealed by the boiling waterprocedure. Moreover, the dye image produced by the invention remainsclearly visible through the glass-like sealed surface provided by theconventional boiling water treatment.

The printed and sealed surfaces produced as described above can beexposed to light in a Fadeometer and are found to provide a degree oflight fastness which one would not normally associate with a dye havingsublimable characteristics. In this manner, the product of the inventionis unexpectedly adapted for prolonged use in exposure to light as wellas adverse weather conditions.

The process steps associated with the present invention in printing afour color design on anodized aluminum are illustrated in FIG. 3 of thedrawing. Referring now thereto, metal, such as aluminum, after beingcleaned is anodized in step 11 to produce a surface having a porousanodic film. Surface 16 on base alloy 17 having pores 18 (greatlyenlarged) is shown in FIG. 1. Surface 16 is then rinsed with water instep 12 and dried in step 13. In step 14 substrate 19 having imprintedthereon areas 20 (all as shown in FIG. 1) is positioned face down onanodized surface 16. Printed areas 20 are in mirror image of the desireddesign and are imprinted with inks containing dyes with sublimationcharacteristics as set forth hereinbefore. Heat is applied to thenon-face side 21 of substrate 19 to transfer dye to anodized poroussurface 16. The printed substrate is removed and the anodized surface issealed resulting in a sealed and decorated anodized surface 22 as shownin FIG. 2. In contrast to the simple five-step procedure of the presentinvention is the complex operation, illustrated in FIG. 4, which istypical of dip-dyeing processes of the prior art. The operations ofmasking 23, dipping 24, fixing 25, and unmasking 26 must be carried outfor each color. Each time these opertions are done, care must be takenin registration so as to maintain the integrity of the image. Each timethese operations are performed, one must also carefully select materialsand processes so as not to disturb what has gone before. As a matter offact, in some commercial practices, fixing constitutes sealing theanodized surface, which step is followed by the steps of etching ofselected areas and reanodizing. By means of the present invention allregistration is taken care of by the printer, the expert in this art.All colors go on simultaneously. The process operations of the presentinvention are the same whether one, two, four or twenty colors are used.No care need be exercised to protect prior deposits. Thus the presentinvention provides a novel process eliminating substantially all needfor skilled labor in decorating anodized aluminum. From the point ofview of metal treatment, the present invention provides a simple processessentially involving only anodizing to provide a porous surface, heattransfer of an image and sealing by means of hot water, boiling water orthe like to close the pores of the anodized surface and seal the designtherein.

The invention is defined in the claims which follow.

We claim:

1. A process for decorating aluminum with a design having at least onecolor, which comprises anodizing said aluminum to provide a porousanodic layer thereon, contacting said porous, anodic layer, afterdrying, with a substrate, face down, having imprinted on the facethereof a mirror image of said design in at least one ink containing acoloring agent having the following sublimation characteristics:

(A) no noticeable sublimation below 120 F.;

(B) a sublimation half-life at 500 F. of less than 75 seconds; and

(C) a sublimation half-life at a temperature in the range of from 140 F.to 500 F. of from 05-75 seconds;

only once while in contact with said dry porous anodic layer, subjectingsaid substrate and its ink impression to a temperature in excess of 140F. for a period of time sufiicient to cause said coloring agent tosublime and condense within said anodized aluminum surface in desginconfiguration and thereafter sealing said anodized aluminum surface.

2. A process as in claim 1 wherein the design is in a plurality ofcolors, the substrate paper and the anodized aluminum is sealed inboiling water.

3. A process as in claim 1 wherein the coloring agent is substantive toan anodized aluminum surface.

4. A process as in claim 1 wherein the aluminum is anodized in anaqueous sulfuric acid electrolyte.

5. A process for decorating aluminum with a design having a plurality ofcolors, which comprises anodizing said aluminum in an aqueous sulfuricacid electrolyte to provide a porous anodic layer thereon, contactingsaid porous, anodic layer, after drying, with a substrate, face down,having imprinted on the face thereof a mirror image of said design in aplurality of inks each containing a coloring agent having the followingsublimation characteristics:

(A) no noticeable sublimation below F.;

(B) a sublimation half-life at 500 F. of less than 75 seconds; and

(C) a sublimation half-life at a temperature in the range of from F. to500 F. of from 0.575 seconds;

only once while in contact with said dry porous anodic layer, subjectingsaid substrate and its ink impressions to a temperature in excess of 140F. for a period of time sufiicient to cause said coloring agents tosublime and condense within said anodized aluminum surface in designconfiguration and thereafter sealing said anodized aluminum surface.

6. A process as in claim 4 wherein the substrate is paper and theanodized aluminum is sealed in boiling water.

7. A process as in claim 4 wherein the coloring agents are substantiveto an anodized aluminum surface.

References Cited UNITED STATES PATENTS 3,172,786 3/1965 Kirby et a1.204-35.1 X 3,264,158 8/1966 Howe l486.1 X

FOREIGN PATENTS 137,036 3/1961 U.S.S.R.

OTHER REFERENCES Colour Index, vol. 2, p. 2885, 2876, 1957 edition.

WINSTON A. DOUGLAS, Primary Examiner M. I. ANDREWS, Assistant ExaminerU.S. Cl. X.R. 204--35, 38

